Hot Stuff
Martin GrohmanI recently attended a presentation showing that the percentage of the American family budget devoted to energy and transportation costs increased from 5% in 1998 to 20% in 2008, and is projected to be 40% in 2018. If energy costs do increase, renewable energy is one way to shield yourself from the trend. So after much deliberation, we recently took our first plunge into the renewable energy space, and had solar hot water panels installed on our roof. Sometimes called solar thermal, solar hot water is usually considered the shortest payback renewable energy option. The systems are fairly simple and straightforward, and do not need to be grid-tied like solar electric is in most cases.
We selected a system based on a closed loop recirculating fluid (basically antifreeze) that circulates from the panels back to a superinsulated tank, where the recirculating fluid transfers its heat to the household water supply in a series of coils. While this approach reduces efficiency somewhat, it also reduces the risk of water freezing inside the collector panels, which can happen in a cold climate like ours. On the recommendation of our contractor, we also opted for conventional flat plate collectors, as opposed to the pricier (but higher performance) evacuated tube style collectors. This decision was based on a lack of winter sun hitting the collection area, since, while we are pleased to live up against a preserve with tall trees, those trees shade the house almost completely in the winter (they would probably be in the shade of my chainsaw, but they’re not on our land). So when the sun is low in the sky in the winter, it’s blocked by those trees, and even the highest performance collector will not help that.
After two weeks, I don’t love everything about the new system, particularly that it uses the oil furnace as a backup. There is no equivalent of a programmable thermostat in the design, and in the evening when we don’t need hot water, the furnace will often come on and heat a tank of water for the night. So the timing of when we need the most hot water (for morning showers) vs. when the sun shines and heats the water (later in the day) is a disconnect. This is addressed in part by the large storage capability of the 105-gallon Stiebel Eltron tank the system uses. And to be fair, conventional hot water systems generally have this limitation as well – most conventional hot water systems make hot water whether you need it or not.
But, given all these reservations, how does the system work? I have to say I am very impressed with it. It sounds silly to say, but the sun can make some serious hot water. For example, on a clear fall evening last week (this is well into October in Maine, mind you), on a day when the temperature peaked in the 50’s, we returned from a hike. We all took showers and gave the kids a bath, and the furnace never came on – the panels had made 105 gallons of 130°F water. That is a lot of hot water, and it feels great to let that water run a little and know no dinosaur juice went into making it. Even though it’s late fall now, if we get any sun at all, the panels quickly reach 150°F, and even the slightest amount of light will push them above 100. Plus, In the first week, our power usage was down 54% (which I can tell since I have a smart meter now), showing a major difference from eliminating the electric hot water heater. That is gratifying because of course that’s the source of the payback, a reduced electric bill. Here’s a look at our usage (the panels were installed on September 21):
We’ll see how these usage numbers average out over the next few months, and hope for a lot of sunny days.
Of course, I was very interested in the installation, and in particular how the roofing penetrations would be managed. I was right up there on the roof asking questions! I’m sure they just love clients like me... In any case, one question I asked was what type of roofing the installers preferred, and I was pleased to hear the answer asphalt shingles – on the basis of their good walkability, and ease of repair and modification. I kept a close eye on where they were poking holes in my roof: here’s a look at the cold water supply to the panels (prior to the installation of an insulating boot):
Here’s a mounting bracket:
Looking at the mounting on the roof in more detail, a fairly small number of roofing penetrations are required for the whole system: the brackets for the collectors account for eight of them, and then the cold water in and hot water out, and that’s it. However, I should note that this is not a GAF-approved detail – we recommend flashing or boots around all roof penetrations. Don’t ever rely on a maintenance item like caulk to keep your property dry. I did not catch this in time, so somewhere down the line, I’m probably going to be up on the roof with a tube of Flexseal. And it all speaks to the need to have a professional roofer involved in renewable energy installs.
So what about payback? In my initial analysis, even in my cold climate, I think the system is looking good to pay for itself – I’m getting much more hot water than I expected in October. The system has no problem at all keeping up with the amount of hot water our typical family of four uses, at least if it’s sunny. In fact, if we get any kind of sun at all the panels heat right up, and I’ve noticed that multiple days of sun in a row can really get the whole tank heated to the max (the system can protect itself from overheating, should that ever become a problem). The panels are basically panes of glass over black frames with black finned tubing within, so it isn’t complex, and it’s easy to understand why it works. There’s a temperature gauge in the basement, and I’m like a new dad, always running down there to check it. I’ve even had to show the system to dinner guests. In a warmer, sunnier climates, in my view, the opportunity to go with solar thermal would be even more compelling. Once you have paid the cost of the system, it should be free hot water or close to it, and maintenance costs are projected to be low – the sun’s heating element isn’t going to burn out, after all...
Here’s at look at the finished panels. I think they look great! What do you think? Would you try this on your own home?
Reader Comments (3)
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Just a folllow up, after a nice spring day here in Maine. March 17 sunny and 50 degrees, easily heated our 105 gallon water tank to 145F. System is really working.
Wiring problems will prevent electricity from passing to vital parts of the furnace. Some wires come loose because nuts or tape holding them in place come undone. Technicians must cut any damaged wires and install new wiring.